Electrodeposition is a frequently-used method to deposit different conductive metals into vias for forming electrical connections. Electroplating baths for electrodeposition of metal are typically aqueous solutions comprising metal salts, ionic electrolytes, and myriad additives like accelerators (brighteners), suppressors levelers, etc. The additives play key roles in electrodeposition since inappropriate species or concentrations may lead to voids, insufficient filling, and non-uniform deposit, and such defects can generate adverse effects to the devices, leading to great loss during mass production. For example, FIG. 1A-B show a via with poor filling quality at inappropriate leveler concentration, and another via with good filing quality at appropriate leveler concentration respectively.
As electrodeposition is commonly used for fabrication of electronic components and devices, reliable operation of electroplating baths in a manufacturing process need employ suitable analytical methods for determining the appropriate concentrations of the additives. These analytical methods are often used to determine the concentrations of species in the bath during operation, so as to provide on-line feedback control, and adjust the amount of additive for maintaining concentrations within pre-determined limits as shown in FIG. 2.
U.S. Pat. No. 6,572,753 provides a method for analysis of three organic additives in an acid copper plating bath. Cyclic voltammetric stripping (CVS) methods are used to measure the concentrations of the suppressor and anti-suppressor based on the effects of these additives on the copper electrodeposition rate. The method uses measurements of the copper electrodeposition rate to determine the concentration of the leveler additive. The other two additives are included in the measurement solution at concentrations determined to provide the optimum compromise between minimal interference, high sensitivity and good reproducibility for the leveler analysis. Nevertheless, the method provides only a single analysis for leveler.
U.S. Pat. No. 6,808,611 discloses an electro-analytical method for determining the concentration of an organic additive in an acidic or basic metal plating bath using an organic chemical analyzer. The method includes preparing a supporting-electrolyte solution, preparing a testing solution including the supporting-electrolyte solution and a standard solution, measuring an electrochemical response of the supporting-electrolyte solution using the organic chemical analyzer, and implementing an electro-analytical technique to determine the concentration of the organic additive in the plating bath from the electrochemical response measurements. However, the method provides merely a single analysis for leveler.
U.S. Pat. No. 7,186,326 discloses a method for measuring the concentrations of a suppressor additive and an anti-suppressor additive in a plating bath for electrodeposition of a metal. Suppressor and anti-suppressor additives in an acid copper sulfate plating bath are analyzed by the cyclic voltammetric stripping method without cleaning or rinsing the cell between the two analyses. The suppressor analysis is performed first and the suppressor concentration in the resulting measurement solution is adjusted to a predetermined value corresponding to full suppression. This fully-suppressed solution is then used as the background electrolyte for the anti-suppressor analysis. However, the method provides only a sequential analysis for suppressor and accelerator.
U.S. Pat. No. 7,384,535 provides a method for determining the quantity of both brightener and leveler in a metal plating bath. The method is able to improve the reproducibility of measuring brighteners and levelers in electroplating baths. Nevertheless, the method provides just an integrated analysis for accelerator and leveler.
In actual mass production, two or more inhibitors such as a leveler and suppressor are frequently employed simultaneously in recipes for acquiring good via filling quality. However, the abovementioned methods fail to provide an integrated analysis for two or more inhibitors simultaneously. The problem raised here is that the sum of concentrations of at least two inhibitors is not equivalent to the measured concentration since the inhibitors provide other inhibiting effects when different inhibitors are mixed in a plating solution. For example, according to the prior art, when simply considering the equivalent concentration of two inhibitors by the sum of concentrations of each inhibitors, such calculation fails to provide the same results as the measured inhibitor concentration during the mass production, thereby leading to error occurred as shown in Table 1:
TABLE 1Actual SMeas. SSampleconcentration concentrationError18 ml/L11.5 ml/L43.91%25 ml/L6.59 ml/L38.13%
As shown in Table 1, the error generated can be as large as to be 43%. Such shortcoming makes manufacturer incapable of maintaining the appropriate additive concentration during the mass production, thereby substantially lowering the yield of products.
Therefore, there is an unmet need to provide an accurate, fast, and cost effective method for determining the concentrations of at least two inhibitors simultaneously in an electroplating bath during on-line feedback control for appropriate adjustment of the amount of additives in the bath to maintain the additive concentrations within pre-defined limits during device production.